The main objective of these studies is to develop procedures for quantitative determination of three-dimensional displacements of teeth when they are acted upon by known force system (s). The displacements of teeth will be measured in-vivo using the modern, noninvasive technique of laser hologram interferometry; determination of the necessary parameters will be enhanced by development and use of the automated system for interpretation of holograms. These displacements will, in turn, be related to quantitative and qualitative biological changes in response to orthodontic forces. The significance of these studies lies in the fact that they will provide adequate information to develop relationshis between the three-dimensional tooth motion, the force system, and time. Thereby, centers of rotation under varying load conditions will be determined.